The present invention relates to an electric power system.
A conventional battery protective circuit for secondary batteries connected in series is disclosed in Japanese laid-open Patent Publication Hei 8-78060.
FIG. 11 is a view showing a modification of the conventional battery protective circuit of Japanese laid-open Patent Publication Hei 8-78060. In FIG. 11, reference numerals 1101 indicate secondary batteries, 1102 voltage detection circuits, 1103 resistors, 1104 comparators, and 1105 an FET.
The two secondary batteries 1101 are connected in series and the voltage detection circuits 1102 are connected across the respective secondary batteries 1101. To each input of the comparators 1104, a reference voltage by the divided voltage of the resistors 1103 connected in series and the output of the voltage detection circuits 1102 are connected respectively.
Both output of the comparators 1104 are connected to the gate of the FET 1105 inserted in series with the secondary batteries 1101.
The voltage detection circuits 1102 detect the voltages of the secondary batteries 1101 respectively and the comparators 1104 compare the detected value with the reference voltage by the divided voltage of resistor. When any of the secondary batteries 1101 is fully charged and the detected value of any of the voltage detection circuits 1102 is more than the reference voltage, the output of any of the comparators 1104 becomes low revel, and the FET 1105 is turned off, and the charging is stopped.
The conventional battery protective circuit requires the exclusive voltage detection circuits 1102 respectively for the two secondary batteries 1101 connected in series. The reason is that the potential levels of the detected values of the voltage detection circuits 1102 are different from each other on the basis of the lowest negative terminal of the secondary batteries 1101 connected in series.
The voltage division resistors 1103 must be also installed exclusively for the secondary batteries 1101 respectively.
The values of the resistors 1103 are always varied from the nominal value within a certain range in the production process, so that the reference value for specifying full charging is also varied and the precision of the reference voltage is lowered.
Further, to make the different potential levels of detected values of the voltage detection circuits 1102 equal by level-shifting, the comparators 1104 must be installed exclusively for the secondary batteries 1101 respectively. Moreover, the withstand voltages of the comparators 1104 must be equal to the total voltage of the batteries connected in series.
Even if a circuit fulfills the same function for each of the secondary batteries like this, a circuit fit to each potential level is required for each of the secondary batteries. Accordingly, assuming that a plurality of batteries 1101 are additionally connected in series, the number of circuits increases and the cost, size, and power consumption also increase. Parts of the comparators 1104 having a withstand voltage meeting the total voltage of the batteries connected in series do not exist actually and it is difficult to realize this circuit.
The electric power system of the present invention has a plurality of capacitors connected in series, a plurality of DC-AC conversion circuits for converting and outputting each DC voltage of the plurality of capacitors to an AC signal that an AC component equivalent to the inter-terminal DC voltage of each of the capacitors is superimposed on the each DC voltage, a plurality of condenser couplers for breaking the each DC voltage from each output of the plurality of DC-AC conversion circuits and outputting the AC components respectively, and a processing circuit for selecting each output of the plurality of condenser couplers and detecting the inter-terminal DC voltage of the corresponding capacitor from the selected AC component.
The electric power system of the present invention has a plurality of capacitors connected in series, a plurality of DC-AC conversion circuits for converting and outputting each DC voltage of the plurality of capacitors to an AC signal that an AC component equivalent to the inter-terminal DC voltage of each of the capacitors is superimposed on the each DC voltage, a plurality of condenser couplers for breaking the each DC voltage from each output of the plurality of DC-AC conversion circuits and outputting the AC components respectively, a processing circuit for selecting each output of the plurality of condenser couplers, converting the selected AC component to a digital signal, and detecting the inter-terminal DC voltage of the corresponding capacitor from the digital signal, wherein the processing circuit has a selection circuit for selecting output from the plurality of condenser couplers, an A-D conversion circuit for converting the selected AC component to a digital signal, and a microcomputer for detecting the inter-terminal DC voltage of the corresponding capacitor from the digital signal.
The present invention is an electric power system, wherein the processing circuit has an AC-DC conversion circuit for converting the AC component selected by the selection circuit to a DC voltage which is full-wave rectified and supplies the converted DC voltage to the A-D conversion circuit.
The present invention is an electric power system wherein the plurality of DC-AC conversion circuits have a plurality of control power sources for outputting a voltage higher than the inter-terminal voltage of the plurality of capacitors and perform the conversion operation of the plurality of DC-AC conversion circuits by the output of the plurality of control power sources.
The present invention is an electric power system, wherein the control circuit has a plurality of voltage control voltage sources for outputting a voltage proportional to the inter-terminal voltage of each capacitor of the plurality of capacitors and the output of the plurality of voltage control voltage sources is used as a power source of the AC-DC conversion circuit, and wherein the control circuit has a storage circuit for storing a correction formula and the output of the A-D conversion circuit is correction-operated by the microcomputer on the basis of the storage contents of the storage circuit.
The present invention is an electric power system, wherein each circuit of at least a part of the DC-AC conversion circuit, condenser coupler, and control circuit is each enclosed by an insulating trench formed on the substrate.